The present invention relates to improving reliability and maintenance of an air purification device by providing a protective cover for a needle-shaped electrode used for ozone generation in the device.
Air purification devices have been available for the purpose of purifying and deodorizing air where good air quality is demanded. Some examples of these areas are residences with asthma patients, lavatories, and clean rooms, to name a few. An air purification device is generally provided with at least two electrodes, between which a high voltage is applied to develop a corona discharge across an air gap, whereby oxygen is transformed into ozone.
Some low-cost air purification devices, mainly aimed for residential use, have a relatively simple structure comprising a needle-shaped electrode having a pointed tip and an opposite electrode in the shape of a hollow cylinder. Japanese published applications JikkaiS63-103729 and JikkaiH04-110725 disclosed such a structure, wherein the needle-shaped electrode is positioned along the cylindrical axis of the opposite electrode with the pointed tip pointing toward the opposite electrode. This type of structure has an advantage of generating ion wind from one opening to the other of the hollow cylinder with the application of a DC voltage, thus eliminating the need for a fan for diffusing ozone.
Reliability and efficiency of air purification devices, however, greatly suffer when the electrodes are exposed without protection in an offensive environment such as in the presence of ozone and corona. For example, the chemical as well as physical reactions with ozone or corona as well as the sputtering effect damage the metal surface, requiring frequent replacement of the needle-shaped electrode. Furthermore, dust or contaminants tend to collect between the two electrodes, requiring frequent cleaning that involves disassembling and reassembling the device.
Some measures taken by the prior art include the use of a detachable cartridge for one or both of the electrodes for easy cleaning, as disclosed in TokkaiH10-291807, Tokkai2001-80908, and Tokkai2000-82567, for example.
However, the additional structure such as above is primarily meant for the purpose of cleaning the inside of the opposite electrode having the shape of a hollow cylinder. Since the electric field is strong especially around the pointed tip of the needle-shaped electrode, this electrode tends to collect more dust or contaminants at the tip, requiring more frequent cleaning than the opposite electrode. To address both the dust collection problem and the degradation problem of the needle-shaped electrode, Japanese Patent 2541857 disclosed ceramic coating, preferably quartz, to protect the needle-shaped electrode. This patent relates to an ion generator that is primarily used for discharging charged particles in a clean room in semiconductor fabrication facilities. However, as noted in Tokkai2001-189199, in order to develop a corona discharge using the needle-shaped electrode coated with ceramics, the applied voltage has to be increased, thereby causing unwanted noises due to electromagnetic radiations.
In considering above circumstances surrounding the use of a needle-shaped electrode in an air purification device, we recognize that a new measure is desired to protect the needle-shaped electrode from the chemical and physical reactions with ozone and corona and from the sputtering effect, as well as to provide ease of maintenance, without drastically changing existing settings such as applied voltage values. Furthermore, the desired measure has to be cost-effective so as not to defeat the original purpose of low-cost air purification for residences. The present invention therefore addresses a new, low-cost protection means for the needle-shaped electrode to improve product reliability, while providing ease of maintenance, of air purification devices.
In accordance with the present invention, there is provided an air purification device comprising: a first electrode in the shape of a hollow cylinder having one open end and an other open end; a second electrode in the shape of a solid needle having a tip end portion of a predetermined length including a pointed tip and an other end portion, the second electrode being positioned along a cylindrical axis of the first electrode, with the pointed tip pointing toward the first electrode and the other end portion of the second electrode being outside of the one open end of the first electrode; a dielectric member covering the second electrode except the tip end portion; and a power supply for applying a high voltage across the two electrodes in order to create a corona discharge, for ozone generation and for generating ion wind that flows out through the other open end of the first electrode. The second electrode is positioned by a non-conductive holding member, which is either detachably or integrally attached to the dielectric member.
The length of the second electrode and the size and shape of the dielectric member covering the second electrode are such that a sufficient space is provided for airflow to be permitted through the one open end of the first electrode where the second electrode is positioned. The predetermined length of the tip end portion of the second electrode is in the range of 0.1 mm to 1 mm. The dielectric member is comprised of either plastic (including epoxy) or silicone.
The thickness and the shape of an end portion of the dielectric member, closest to the pointed tip are such that, in case a person touches the pointed tip with his finger, the end portion of the dielectric member prevents penetration of the tip end portion of the second electrode into the skin of the finger.
As an example of the shape of the dielectric member, there is provided a circular flange concentrically covering the second electrode except the tip end portion. The flange comprises a portion with a first diameter and a portion with a second diameter, the second diameter being larger than the first diameter, and the portion with the second diameter facing away from the first electrode.
According to one embodiment, the air purification device comprises a plurality of pairs of the first electrode and the second electrode. The second electrodes are positioned by the respective non-conductive holding members which are connected integrally; and the second electrodes are covered, except the respective tip end portions, with the respective dielectric members which are connected integrally.